Improved door construction has been for thousands of years a matter of continuing interest and remains of interest today. Invariably the environment in which the door is to be utilized dictates the nature of the doors construction. The galley of modern aircraft is an environment in which there are many compartments, some of which house refrigerators or freezers. The requirements that doors for galley refrigerator/freezer compartments must meet are different than refrigerator/freezer doors located in other non-airborne environments. Of primary concern in aircraft galleys is the fact that the crash of the aircraft must be considered. When this possible happening is taken into account, it will be appreciated that the refrigerator/freezer door must be able to withstand sudden impact loading of the refrigerator/freezers entire contents against the inside of the door, should the plane go down. Absent the presence of a door with sufficient strength, the contents would be converted into deadly missiles within the aircraft cabin.
Those individuals familiar with aircraft galleys are no doubt impressed by the compactness of the equipment and the relatively small area within which the flight attendants must move. It is not uncommon to open and close a galley compartment door during a flight a dozen or more times. Typically, compartment doors are provided with a latch mechanism positioned midway along the edge of the door. This latch location optimizes the doors capacity to handle a sudden impact loading experience from within. The location of the latch as just described, however, gives rise to a practical problem of insuring that the door is latched after every usage. The doors of the prior art invariably required a delivering of a direct force to the door from a point in the immediate vicinity of the latch in order to cause the latch to be secured. Aircraft cabin attendants are frequently in a rush, especially on flights of short duration where passenger serving time is limited. These attendants, when rushed on most occasions, hit the door at an upper corner or use their knee to push the door to a closed and latched condition. This point loading of the door is most often not delivered to the door front near the latch. In order that the refrigerator/freezer door be provided with a sealed environment, there is provided between the door and the refrigerator/freezer compartment surface, against which the door is closed, a resilient strip of material. When, for example, the door is normally pushed closed with point pressure applied at an upper corner of the door, the resilient material is compressed and the force transmitted through the door to the latch mechanism. If the door is not extremely stiff, the door tends not to fully latch. It is therefore believed apparent that an ideal door should be torsionally stiff and capable of withstanding a sudden loading from within. The door closing procedure outlined above has resulted in prior art doors being repeatedly flexed or racked back and forth until the door finally becomes structurally loose, weak and will not latch.
Merely making the door stronger by making it of heavier material is an unacceptable solution. In the past, when aircraft fuel was cheap, the weight of such doors was not critical. Some aircraft manufactures today assess the fuel cost per pound over the useful commercial life of an aircraft at $150.00 per pound or more. The door embodying the invention to be described hereinafter provides a door that is several pounds lighter than is presently available in the market place. The door is torsionally stiff and can withstand a possible impact loading from within, without structurally failing.
As noted at the outset, door construction has been evolving over the years. New materials that are light and strong, such as fiberglass and foam insulation, have found their way into door construction. Typical of such a door having a rigid plastic skin made of a polyester resin glass fiber mixture and filled with insulating foam, is that found in the Vincent Di Maio Pat. No. 3,950,894. The Di Maio door is intended for use as an architectural door for a dwelling. Although the Di Maio door is light in weight and insulated, no provision is made for the door to withstand internal impact loading and point applied closing forces to its outside. All structural features which overcome the problems of impact loading and point applied closing forces are incorporated in the door of the preferred embodiment of the invention to be described more fully hereinafter.
The patent to Slopa, et al, U.S. Pat. No. 2,652,601 is a typical refrigerator door of the prior art which recognizes the utility of providing diagonal sheet metal stripes 25 across the face of the door to make the door more resistant to torsional loading. The Slopa, et al refrigerator door does not, however, suggest as the invention to be described contemplates, intersecting support members within a door in which support members are secured to spaced apart panels which comprise the front and rear panels of the refrigerator door.
By way of further example of the prior art, the patent to Donald D. Andresen, U.S. Pat. No. 4,294,055 is directed to a honeycomb overhead door with stiffening members 34 and 36. Each of the stiffening members 34, 36 are made up of a honeycomb core 38 which is covered by opposite strips 40. While these stiffeners 34, 36 as shown are sandwiched between plywood veneer, there is no appreciation of the advantageous consequences of bonding a channel shaped support member to a pair of spaced apart panels as the invention to be described provides.
Although the patent to Harman, U.S. Pat. No. 3,720,032, is directed to a lightweight panel construction in which there are provided concentrically disposed corrugations of rectangular cross-section between plastic front and rear panels 14, 16, there would be no motivation to use the panel as a refrigerator door even with the diagonal tensioning members 24, because though the door so formed would be light in weight, it would not provide a torsional stiff door structure of the type required.